1. Field of the Invention
The present invention relates to a multi-layered inductor array including a plurality of inductors.
2. Description of the Related Art
A conventional multi-layered inductor array 1 is shown in FIG. 5. The multi-layered inductor array 1 includes magnetic sheets 2 having coil conductors 3a to 6e provided thereon. The coil conductors 3a to 3e are electrically connected in series to each other through via-holes 12 formed in the magnetic sheets 2 to define a spiral inductor L1. Similarly, coil conductors 4a to 4e, 5a to 5e, and 6a to 6e are also electrically connected in series to each other through the via-holes 12 formed in the magnetic sheets 2 to define spiral inductors L2, L3, and L4, respectively.
The individual magnetic sheets 2, as shown in FIG. 5, are laminated together, and on the upper and lower portions of the laminated magnetic sheets 2, magnetic cover sheets (not shown) having no conductors provided on the surfaces thereof are disposed. Then, the laminated magnetic sheets 2 are integrally fired to define a multi-layered structure 15 as shown in FIG. 6. On the front and back side-surfaces of the multi-layered structure 15, external electrodes 21a to 24a and 21b to 24b of the inductors L1 to L4 are disposed, respectively.
In the multi-layered inductor array 1, to reduce the size of the inductor array 1, when the inductors L1 to L4 are arranged close to each other in the multi-layered structure 15, independence between the magnetic paths of the inductors L1 to L4 is reduced, and as a result, magnetic couplings between the inductors L1 to L4 occur. Thus, the inductors L1 to L4 in the multi-layered structure 15 have different inductance values.
As shown in FIG. 7, since the magnetic paths of the spiral inductors L1 and L4 disposed on the right and left end surfaces of the multi-layered structure 15 are narrower at the end surfaces thereof, the inductance values of the inductors L1 and L4 are reduced. To solve this problem, the number of winding turns of the spiral inductors L1 and L4 is increased as compared to that of the spiral inductors L2 and L3, and the diameters of the spiral portions of the inductors L1 and L4 are increased as compared to those of the inductors L2 and L3, to compensate for the reduction of the inductance values. However, since the lengths of the coil conductors of the inductors L1 and L4 are different from the lengths of the coil conductors of the inductors L2 and L3, the DC resistance values of the inductors L1 to L4 differ.
In order to overcome the above-described problems, preferred embodiments of the present invention provide a multi-layered inductor array that minimizes variations in the inductance values and DC resistance values of three or more inductors provided in a multi-layered structure.
According to a preferred embodiment of the present invention, a multi-layered inductor array includes a multi-layered structure defined by a laminated body of a plurality of magnetic layers and a plurality of coil conductors, at least three spiral inductors provided by electrically connecting the coil conductors to be aligned inside the multi-layered structure, and external electrodes disposed on surfaces of the multi-layered structure that are electrically connected to leading end portions of the plurality of spiral inductors. In this multi-layered inductor array, the plurality of spiral inductors have an equal number of winding turns, and, in the direction in which the spiral inductors are aligned, the lengths of the spiral portions of the inductors positioned at both end portions of the multi-layered structure shorter than the length of the spiral portion of the remaining spiral inductor.
Because magnetic paths of the spiral inductors positioned at both end portions of the multi-layered structure are narrow on the end surfaces thereof, the inductance values of the inductors is reduced. However, since the lengths of the spiral portions of these inductors positioned at both end portions of the multi-layered structure are shorter than the length of the spiral portion of the remaining inductor, the inductance values of the spiral portion of the remaining inductor is adjusted to also be reduced. Thus, variations in the inductance values between the spiral inductors are greatly suppressed.
Other features, elements, characteristics and advantages of preferred embodiments of the present invention will become apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.